1. Field
One embodiment of the invention relates to a printed circuit board having a frame ground portion.
2. Description of the Related Art
In small electronic devices such as portable computers and personal digital assistants, which have electronic circuits incorporated in their housings, a frame ground (FG) for connecting the ground of the electronic circuit to a metal frame is an essential structural element. The ground of the electronic circuit determines reference for operating voltage, and functions as a return path for operating current. A weak frame ground may lead not only to instability of the reference voltage of the electronic circuit and unnecessary radiation but also to erroneous operation due to external noise or electrostatic discharge. In particular, the frame ground in which a copper foil pad is formed around a board-fixation hole requires frame ground technology in order to avoid ground connection failure caused by copper foil oxidation.
Heat treatment in normal surface mount technology (SMT) does not cause oxidation to such a degree that the copper foil pad of the frame ground is discolored. However, in conditions of high temperature heat as in baking, the copper foil pad of the frame ground tends to oxidize, leading to conduction failure of the frame ground. As a technology for preventing such conduction failure, gold plating of a pad surface is known. However, gold plating is expensive and hence increases manufacturing costs.
In Jpn. Pat. Appln. KOKAI Publication No. 2001-251029, another technology for preventing conduction failure caused by such oxidation is proposed. In this technology, a plurality of mounds of solder are applied to a copper foil land formed around the board-fixation hole of a frame ground and a screw is inserted in the hole so that the head of the screw is in contact with these mounds of solder, thereby maintaining a satisfactory ground connection in the frame ground.
However, the conventional frame ground technology in which mounds of solder are applied to a copper foil pad thickens the frame ground and discourages further reduction in size, especially in devices that require a lightweight, thin, and small design.